This study was concerned with the developmnt and establishment of pure cerebrovascular smooth muscle culture. The established cell line originals from dissociated cells of microvessels obtained from brains of rats by mechanical dispersion and filtration technique. The cultured cells display histochemical and ultrastructural features characteristic of smooth muscle cells. They are as follows: an ovoid nucleus with one to four nucleoli and a granular slightly basopohilic perinuclear cytoplasm which is slightly PAS-positive; prominent myofilaments, many of which are arranged in bundles throughout the cytoplasm, prticularly adjacent to the opposing cellular membranes of the cells. In view of these observations, the cultured cerebrovascular smooth muscle cells provide a new model system for studying their function, especially related to the function o cerebral blood flow, blood pressure and overall to the blood-brains barrier function.